Conventional Ion Implantation Research Articles

Simulation of dose uniformity for different pulse durations during inner surface plasma immersion ion implantation

Without the line-of-sight limitation, plasma immersion ion implantation (PIII) emulates conventional beam-line ion implantation in inner surface modification of industrial components. However, dose uniformity on the inner surface is critical. Inner surface PIII of a cylindrical bore is modeled using a two-dimensional fluid model. It is found that the retained dose is not uniformly distributed on the inner surface and the maximum dose is observed away from the edge. The exact location of the maximum dose, which varies with the implant pulse duration, is closer to the center when the pulse width is longer. The maximum relative difference of the retained dose along the interior also depends on the implant pulse duration. It is smaller for a longer pulse duration after a threshold value has been exceeded.

Special modulator for high frequency, low-voltage plasma immersion ion implantation

Plasma immersion ion implantation is a burgeoning surface modification technique and not limited by the line-of-sight restriction plaguing conventional beam-line ion implantation. It is therefore an excellent technique to treat interior surfaces as well as components of a complex shape. To enhance the implant uniformity and increase the thickness of the modified layer, we are using a high frequency, low-voltage process to achieve high temperature and dose rate to increase the thickness of the modified layer. The low voltage conditions also lead to a thinner sheath more favorable to conformal implantation. In this article, we will describe our special modulator consisting of a single ended forward converter with a step-up transformer. The modulator is designed to operate from 5 to 35 kHz and the output voltage is adjustable to an upper ceiling of 5000 V that is deliberately chosen to be our voltage limit for the present experiments. We will also present experimental data on SS304 stainless steel materials elucidating the advantages of our modulator and high frequency, low-voltage experimental protocols.

Application of plasma immersion ion implantation doping to low-temperature processed poly-Si TFTs

This work applied, for the first time, plasma immersion ion implantation (PIII) for source/drain doping on low-temperature processed polysilicon thin-film transistors (poly-Si TFTs). Experimental results indicate that PIII doping can provide adequate dopant concentration and junction depth for source/drain. In addition, H/sub 2/-diluted phosphorus PIII can promote dopant activation more efficiently during RTA at 600/spl deg/C than with conventional ion implantation (II) technology. The excellent characteristics of PIII doped poly-Si TFTs resemble those of conventional II doped ones.

Characterization of TiN films alternately treated with PVD and Cr ion implantation

The projected ranges of the conventional ion implantation are generally below submicrons. This makes it difficult to apply the implantation techniques to the tribological uses. The combined process of the physical vapor deposition (PVD) and the ion implantation was developed to form the thick implanted layers over a few microns. In this process, firstly, the PVD films are deposited by the cathodic arc ion plating method with a film thickness of 50 to 250 nm. Secondly, the metal ions are implanted using the pulsed arc ion source at an energy below 80 keV without mass separation. These two processes were alternately conducted up to the film thickness of a few microns. Using this combined process, Cr implanted PVD-TiN films were studied. The film thicknesses of the implanted layers were 2–7 μm, which are over ten times larger than those of conventionally implanted layers. Furthermore, these films showed excellent wear resistances compared with the unimplanted PVD-TiN films.

Characterization of ultra-shallow p + -n junctions formed by plasma doping with BF 3 and N 2 plasmas

Plasma doping (PLAD) is a promising alternative to conventional ion implantation for the formation of ultra-shallow p + -n junctions. In the PLAD process, a silicon wafer is placed directly in a plasma containing the desired dopant ions and then pulse-biased to a negative potential to accelerate positive dopant ions into the silicon surface. Most of Varian's work to date has used BF 3 source gas and wafer biases of −0.5 to −5 kV to implant boron into 150 and 200 mm wafers. Data will be presented showing successful formation of ultra-shallow junctions, good sheet resistance uniformity and repeatability, and excellent structural quality of the silicon after rapid annealing. Very good device characteristics obtained from deep sub-half micron MOSFETs fabricated using PLAD will also be shown. Finally, the combination of PLAD with an N 2 plasma followed by ultra-low energy B + implantation to produce ultra-shallow junctions with low sheet resistances will be discussed.

Current status of single ion implantation

The current status of single ion implantation (SII) which has been proposed as a novel technology to suppress the fluctuation in dopant number in fine semiconductor structures is reported. The key to control the ion number is to detect secondary electrons (SEs) emitted from a target upon ion incidence. By improving the SE detection system, we have achieved the efficiency of 90% which ensures the reduction in the fluctuation of dopant number to 30% compared to the conventional ion implantation. The improvement for the better SE detection efficiency has turned out to also be effective for the precise beam alignment. The single ion incident position can now be successfully controlled with an error of less than 0.3 μm.

Treatment uniformity of plasma immersion ion implantation studied with three-dimensional model systems

Plasma immersion ion implantation is a rapidly developing technique for ion-beam treatment of materials, mainly metals and semiconductors. This technique was developed initially to circumvent the line-of-sight restrictions of conventional beam-line ion implantation. In contrast to the latter, the treatment of three-dimensional samples does not require complicated manipulation of the workpiece and ion beam. With this concept, knowledge of treatment homogeneity is of particular importance for the further development of plasma immersion ion implantation. In the present paper, homogeneity measurements of model systems are discussed. Silicon wafer segments mounted on wedge-shaped and V-shaped sample holders with different edge angles (30° to 120°), and on a U-shaped sample holder (trench), were treated by plasma immersion ion implantation with argon ions of −45 kV high-voltage pulses. The samples were analysed for lateral implantation concentration by Rutherford backscattering spectrometry measurements. The results show that, for wedge-shaped samples, gradients in concentration of implanted argon by a factor of up to six develop, depending on the process parameters. In the case of trenches, differences of more than an order of magnitude between the implantation concentrations of the side walls and bottom of the trench were found.

Plasma-immersion ion implantation

Plasma immersion ion implantation (PIII) is a technique for surface modification. In contrast to conventional ion implantation techniques, the target is surrounded by the plasma and then pulse biased to high negative voltages. In this paper, the principle of plasma and high voltage generation will be shortly reviewed. Further on, the paper concentrates on experiments that have been carried out at Frankfurt university. We report on measurements of surface sputtering occuring during oxygen and argon implantation into silicon targets. Surface sputtering accounts for dose limitation of implanted ions. By combining vapor-deposition of neutral atoms with implantation and diffusion layers of stoichiometric silicon and oxygen ratio with a thickness of more than 300 nm have been obtained. Other experiments in which vapor-deposition only is applied will demonstrate the potential of this simple setup.

Modification of mechanical and chemical surface properties of metals by plasma immersion ion implantation

Plasma immersion (ion) implantation (PII) was developed a decade ago for modifying mechanical and chemical surface properties of metals. In analogy to conventional beam-line ion implantation, it uses energetic ions, mostly nitrogen, that are implanted in the near-surface region of a material. A sample is enveloped by a plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. This process takes place at all sides of the sample simultaneously without requiring ion beam and sample manipulation, in contrast to beam-line ion implantation. The present review discusses the fundamentals of PII and its most important features. The influence of the most important process parameters such as implantation dose, ion density, pulse repetition rate, and sample temperature on hardness and wear resistance and on corrosion resistance of metals and alloys such as mild steel, stainless steel, nickel, aluminium and titanium alloys is discussed.

Distributed electron cyclotron resonance plasma immersion for large area ion implantation (invited)

Plasma-based ion implantation (PBII) is a recent method to implant ions into materials for modifying surface properties. Negative high voltage pulses are applied to the substrate to extract ions from the plasma and accelerate them directly onto the substrate surface. The main advantages of PBII over ion beam implantation are its simplicity for processing large surfaces or three-dimensional objects, and the possibility of preparing surfaces at low ion bombardment energy prior to the implantation process. However, in contrast to conventional ion implantation, the PBII process does not apply mass selection. Due to the wide ion sheath expansion (a few tens of cm), large volumes of plasma are mandatory around the substrate. Multipolar discharges, which produce a peripheral ionization facing the substrate and can be easily scaled up, are well adapted to the PBII process and thus widely used. However, hot filaments to sustain plasmas of reactive gases in multipolar magnetic field structures are progressively phased out in favor of distributed electron cyclotron resonance (DECR) plasma sources. The principle, the design, and the performances of DECR plasmas are presented. Then, PBII in DECR plasmas is illustrated through two selected examples.

Improvement of the wear and corrosion resistance of oil pump materials using plasma immersion ion implantation

A typical oil pump used in oil wells consists of a piston column, piston sleeve and ball valve. The working environment in an oil field is harsh and unforgiving, and the piston column in the oil pump is very vulnerable to wear and corrosion. Hence, improving the wear and corrosion resistance of the piston which is made of 45 # steel is critical to the efficiency and profitability of oil companies. Even though ion implantation is an effective means to enhance the surface properties of the materials, the irregular shape and large dimension of the column make conventional beamline ion implantation very difficult. As the technique of plasma immersion ion implantation circumvents this line-of-sight restriction, it is a suitable technique to improve the wear and corrosion resistance of the components in an oil pump. A treatment process involving RF plasma nitriding and ion beam enhanced deposition (IBED) has been developed. The microhardness, mass loss due to wear, and coefficient of friction of the untreated and treated samples were measured. A salt fog test was also conducted to evaluate the resistance against rusting. The results indicate that the treatment improves the wear and corrosion resistance of the 45 # steel samples significantly, and that the combined RF plasma nitriding and IBED process is more effective than a single RF plasma nitriding step.

Self-aligned subchannel implant complementary metal–oxide semiconductor devices fabrication

High-speed and low-power complementary metal–oxide semiconductor devices with subchannel implants have been proposed and demonstrated recently. In subchannel implant devices, the alignment of the gate and the buried implant region is a critical issue. In this article, a fully self-aligned gate and subchannel implant fabrication method is proposed using either focused-ion-beam or conventional ion implantation. This method defines the gate and produces the subchannel implant in the same step. By doing this, the buried implant region and gate are automatically aligned. By exposing the resist with a B+ ion beam, we verified that the dose needed to produce the subchannel implant matches the dose needed to expose the resist (1013 ion/cm2). We have simulated the implant profile and the expected device performance. The subthreshold current was found to be decreased by 1–2 orders of magnitude. Since the process requires implantation through the gate oxide, capacitors were built over the gate oxide for C–V measurement and implanted over a range of doses. Proper postimplantation treatment has been developed to prevent increasing of the interface state density.

Utilization of plasma source ion implantation for tribological applications

Plasma source ion implantation (PSII) has been developed as an alternative technique to circumvent the limitations of conventional ion implantation, such as the requirements of complicated target handling and beam raster systems for a uniform ion implantation of three-dimensional samples. By applying negative high voltage pulses, positively charged ions are accelerated to and implanted into the target. The plasma sheath expansion and ion doses, calculated with a theoretical model, are in good agreement with the experimentally obtained data. As the analytical model describes the experimental data sufficiently, it is used to discuss design specifications for PSII systems. Furthermore, the possibility of implanting ions into large, three-dimensional samples is discussed on the basis of predictions of the analytical model. The results of nitrogen PSII treatment of planar samples are shown. Wear and hardness of the implanted and unimplanted flat steel samples with a high chromium content were measured. An increased hardness as well as a decreased wear was obtained.

Lateral implantation homogeneity of wedge-shaped samples treated by plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is a rapidly developing technique for ion implantation in metallurgical and semiconductor applications. In contrast to conventional beam-line ion implantation, the treatment of three-dimensional samples does not require complicated workpiece and ion beam manipulation. However, recent results have shown that, in addition to the shape of the workpiece, treatment homogeneity is strongly dependent on process parameters such as ion density and gas pressure. Knowledge of homogeneity is of great importance for the further development of PIII. In the present paper, homogeneity measurements of a model system are discussed. Wedge-shaped silicon specimens with different angles (30 ° to 90 °) were treated by plasma immersion ion implantation with argon ions with 45 kV high-voltage pulses. The samples were analyzed for lateral implantation concentration by Rutherford backscattering measurements. The implanted concentration, the projected range and their gradient are a strong function of the edge angle. The results show that for acute angles (30 °), gradients in implantation concentration up to a factor five develop.

Industrial applications of plasma immersion ion implantation

Plasma immersion ion implantation (PI 3) is a new hybrid technology using elements of ion implantation as well as plasma nitriding. In addition, and due to the high energetic ion bombardment, thermal diffusion can be used to obtain thicker layers than in conventional ion implantation. Furthermore, the process can be used in an ion beam enchanced deposition (IBED) mode to produce various kinds of coatings. This enables the treatment to be adapted to the material structure and state and also to the intended service conditions. Furthermore, economic aspects make PI 3 an interesting technique for surface modification of a wide range of materials. An overview of the worldwide activities in the treatment of components and the achieved improvements will be given.

Sputter and diffusion processes in a plasma immersion device

Plasma immersion ion implantation (PIII) is a technique for surface modification. In contrast to conventional ion implantation techniques the target is surrounded by plasma and then pulse biased to high negative voltages. In our experiment the plasma is generated in a radio frequency ion source with inductive coupling (13.56 MHz) and diffuses into the target processing chamber. In this paper we report on the measurements of surface sputtering occurring during oxygen and argon implantation into silicon targets. Surface sputtering accounts for the dose limitation of the implanted ions. By combining vapor-deposition of neutral atoms with implantation and diffusion we obtained layers of stoichiometric silicon and oxygen ratio with thicknesses of > 300 nm.

Homogeneity measurements of plasma immersion ion-implanted complex-shaped samples

It is commonly accepted, that one of the favourable features of plasma immersion ion implantation in comparison to conventional beam-line ion implantation is its ability to treat non-planar samples without complicated workpiece and beam manipulation. Therefore, it is of particular interest to study the homogeneity of PIII treatment of three-dimensional bodies. In the present paper, homogeneity measurements are of PIII treated model systems are discussed. Wedge-shaped specimens (V- and D-shaped) with different angles made of silicon were treated by plasma immersion ion implantation with argon ions. The voltage pulse heights ranged between 30 and 45 kV. The samples were analysed for retained implantation dose by lateral Rutherford backscattering measurements. These show that large gradients in implantation dose develop under the chosen PIII conditions. An explanation for these gradients is a misalignment of electric field lines, crooked near the edges of samples, and ion trajectories, due to the inertia of the ions.

Plasma immersion ion implantation for metallurgical and semiconductor research and development

Plasma Source Ion Implantation, also termed Plasma Immersion Ion Implantation, is a rapidly developing material modification technique for treating the near-surface regions of various kinds of materials. It makes use of high-energy ions which are accelerated by a high voltage pulse from a plasma which wraps the workpiece to be treated. The ions are implanted into the material causing effects similar to those of conventional beam-line ion implantation. Research and development of plasma immersion ion implantation has focused in two main fields, treatment of metals for improved wear and corrosion performance, and modification of semiconductors. The paper discusses examples from both fields, with nitrogen PIII of steels and aluminum, and modification of thin metal films. From the semiconductor field, trenchwall doping, ultra-shallow doping with boron, and oxygen ion implantation for SIMOX formation is treated.

Wear resistance of plasma immersion ion implanted Ti6Al4V

The plasma immersion ion implantation (PI3tm) process has been employed in the treatment of the Ti6Al4V alloy in order to improve its notoriously poor tribological properties. In particular, this study was undertaken with a view to its potential application for the surface engineering of orthopaedic implants.PI3 has been developed over recent years at the Australian Nuclear Science and Technology Organisation (ANSTO). The hybrid nature of this technique combines elements of both ion implantation and plasma nitriding, and has been shown to produce components with unique surface properties and optimum performance characteristics.A detailed study of the PI3 process on the Ti6Al4V alloy has been undertaken. Treatment was carried out in a pure nitrogen atmosphere at temperatures of 350, 450 and 550 °C. In each case, specimens were treated for 5 h, with a high voltage pulse (typically 40 kV) applied directly to the workpiece.Wear resistance of the treated samples was assessed using a standard CSEM pin-on-disc wear machine, with a single crystal ruby ball as the contact tip. Glancing angle X-ray diffraction (GAXRD) was employed to determine the phases present in the surface modified layer. These findings were then compared to those achieved from parallel work with conventionally ion implanted and low temperature plasma nitrided samples.It was established that a high treatment temperature of 550 °C was necessary for substantial improvements in the properties of the Ti6Al4V material. Under these conditions the PI3 technique promoted significant increases in Knoop hardness, and wear resistance an order of magnitude greater than conventional ion implantation. Wear rates were typically reduced by four orders of magnitude compared to those of the untreated Ti6Al4V. This is thought to be associated with the increased mobility of nitrogen in α-Ti at these temperatures, producing a deeper, hardened case. The presence of TiN was observed in the microstructure of PI3 Ti6Al4V samples at all temperatures in the range.

Niobium oxide thin films formed by plasma immersion oxygen ion implantation

In analogy to conventional beam-line ion implantation, plasma immersion ion implantation can be combined with a deposition technique to an ion assisted coating process. The structure and composition of a coating and its interface to the substrate can be modified by ion implantation. By means of electron beam evaporation and oxygen plasma immersion ion implantation niobium oxide films were prepared at low substrate temperatures ( <200 °C). The film composition and thickness were determined by Rutherford backscattering spectrometry. The results show that oxygen plasma immersion ion implantation leads to incorporation of oxygen into niobium in several steps, corresponding to niobium oxide phases with different stoichiometries. By contrast to conventional beam-line ion implantation at low pressures, two channels for oxidation can be distinguished, ion implantation of high-energy species and radiation enhanced in-diffusion of low-energy species from the plasma. The latter is driven by thermodynamic forces.